The present invention relates to the field of a steering apparatus to be used in a drill string during the drilling of a well to control the direction in which the drill penetrates the earth. This invention is an improvement on my prior inventions as shown in U.S. Pat. Nos. 4,394,881 and 4,635,736. In both of these prior inventions an upper sensing assembly and a lower force applying assembly were provided above the drill bit with the upper assembly including a means for sensing the low side of the hole and the lower assembly including means for exerting a transverse thrust to the upper end of the drill bit to control its direction. This allows a relatively straight or vertical well bore to be drilled or to control the slope and direction of any intentional deviation from the vertical.
In both upper and lower assemblies, pistons have been used both as the sensing means and the slave force applying means. In use these pistons, which are subject to substantial vibration during drilling because of the impacts of the drill bit with the formation, have been found to have damaged seals and to leak before the string has to be pulled to replace a worn drill bit. The pulling of the string to replace piston seals in the steering device is expensive and is desired to be avoided.
The present invention also provides for an increase of the forces exerted by the lower assembly against the well bore to be more than the forces exerted between the upper assembly and the well bore.
U.S. Pat. Nos. 3,916,998; 4,071,101; 4,101,179 and 4,220,213 all disclose drilling stabilizers and were clearly distinguished by the present inventor in his most recently issued U.S. Pat. No. 4,635,736.